The invention relates to an exhaust gas aftertreatment system for a vehicle operated by a combustion engine, in particular for a watercraft, to a method for operating an exhaust gas aftertreatment system for a vehicle operated by a combustion engine, in particular for a watercraft, and to a vehicle, in particular a watercraft, having the exhaust gas aftertreatment system and/or for carrying out the method.
Owing to ever stricter exhaust regulations for vehicles and especially also for ships, it is necessary also to reduce the sulphur emissions, e.g., sulphur dioxide, from vehicles operated by combustion engines.
In plant engineering, there is already a known practice of desulphurizing emissions from combustion engines by feeding an aqueous calcium hydroxide solution or calcium oxide solution into the exhaust gas from the combustion engine. By these solutions, the sulphur emissions react to form harmless calcium sulphate. However, using this type of desulphurization on vehicles is difficult owing to the large amount of space which it requires. If a Selective Catalytic Reduction (SCR) catalyst is additionally arranged in the exhaust line of the vehicle downstream of the infeed of calcium hydroxide or calcium oxide, as seen in the direction of flow of the exhaust gas, to reduce the nitrogen emissions from the vehicle, there is the additional problem that calcium compounds come into contact with the SCR catalyst. There, they act as powerful catalyst poisons which significantly reduce the life of the SCR catalyst. Moreover, calcium hydroxide, calcium oxide and calcium sulphate can also have a powerful abrasive action and thus lead to increased wear on individual components of the exhaust line.
In plant engineering, there is furthermore a known practice of desulphurizing the emissions from combustion engines by feeding ammonia into the exhaust gas. By the ammonia, the sulphur pollutants react to form easily decomposed salts, e.g., ammonium sulphate and ammonium hydrogen sulphate, which are then filtered out of the exhaust gas by suitable filters. However, this type of desulphurization requires complex processes, which are difficult to implement especially in vehicles, since ammonium sulphate or ammonium hydrogen sulphate forms only at temperatures below 300° C. and the exhaust gas from the combustion engine is generally at a significantly higher temperature.
Devices for desulphurizing the exhaust gas are furthermore also already known on vehicles. A device for reducing harmful components in the exhaust gas from a combustion engine, in which, in a preferred embodiment, a “sulphur trap” is arranged in an exhaust line of the vehicle, is disclosed by DE 199 55 324 A1, for example. This sulphur trap reduces the sulphur content of the exhaust gas to ensure the operation of an NOx storage catalyst arranged in the exhaust line downstream of the sulphur trap, as seen in the direction of flow of the exhaust gas, and, where applicable, of a particulate filter likewise arranged downstream. Here, regeneration of the sulphur trap is accomplished by measures in the engine, e.g., by changing the intake air throttling, the injection or the exhaust gas recirculation rate. Here, the sulphur trap is arranged in the exhaust line downstream of an exhaust turbocharger.